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Seminar on Urban Earthquake Hazard at BRAC University on 24t

 
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sikandarsiddiqi
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Joined: 26 Jan 2003
Posts: 294

PostPosted: Sun Apr 23, 2006 3:44 pm    Post subject: Seminar on Urban Earthquake Hazard at BRAC University on 24t Reply with quote

IN GOD WE TRUST- PARDON, PROTECT & HELP US LORD

With due respect
Dear Rt.Honorable Prof.Dr.Engr. J.R Choudhury > VC , BRAC University,Dhaka,Bangladesh
&
President, Bangladesh Earthquake Society,Dhaka

Thanks for your invitation to attend a seminar on "Urban Earthquake Hazard - Perceived Seismic Risk Preparedness in Bangladesh".

My attention has been drawn to the specific word 'Perceived' which I think when scientifically matched with the seismic damage assessment over last 600 (six hundred) years will help to redraw Seismic Zoning Map of Bangladesh because the concept on which current SZMB is based is non seismic in character in the event of a major earthquake. A large number of buildings over vast 2/3 rd of land covered by present day zones 2 & 3 will simply face damage beyond repair or collapse as PGA value assigned to each zone is not correct due to many reasons. So the big question is who will be responsible for such a catastrophic disaster in the years to come.? As the earthquake physics itself is a probabilistic physics so instead of making a conservative estimate there should be enough room for 100% factor of safety with enough flexibility in assigning intensity for an area based on Modified Mercalli Intensity Scale (MMIS) because earthquake safety comes first & above all. Maximum
intensity that may be felt in zone 3 is IX on MMIS and the corresponding PGA value is .55g  but the value assigned in current Seismic Zoning Map of Bangladesh (SZMB) is .25g which is the  minimum value for an earthquake of intensity VIII on MMIS. Apart from this Dhaka city has already experienced from time to time earthquakes of intensities VIII and IX over last 500 ( five hundred) to 1000 (one thousand) years as evident from seismic geological signatures found all around it but PGA value assigned to Dhaka city is .15g which corresponds to an earthquake of intensity VII on MMIS which technically means a moderate earthquake and all buildings have been designed accordingly. I can say with reasonable accuracy that all these buildings will fail in the event of a major earthquake of intensity VIII or IX . Let it be examined why it is so as follows: (MMIS)

a) Earthquake of intensity VII may generate PGA between  .10g to .15g

b) Earthquake of intensity VIII may generate PGA between  .25g to .30g

c) Earthquake of intensity IX may generate PGA between    .50g to .55g

Over mobile phone,some few months back, I discussed this problem with  Prof.Dr.Engr.M.Jahangir Alam of Chittagong University of Engineering & Technology who expressed the same opinion.So I would like to say that a positive decision be taken in an emergency meeting of BES to resolve the problem in saving the country i.e we are to make Bangladesh Totally Earthquake Resistant (BTER) based on Performance Based Analysis/Pushover analysis (PBAPA) and the grading and status of the design should be like that of modern skyscrapers in San Francisco considered to be the most sophisticated earthquake proof buildings in the world vibrated side wise like corn stalks in a strong breeze during an earthquake on Oct. 17. '89 which measured 7.1
on the Richter Scale. The epicenter was only 97 km ( 65 miles ) away on the San Andreas Fault Line which runs through Crystal Springs Reservoir along the western coast of California,USA.

All these reactions are based on the reasonable belief that most of the smart buildings being built in Dhaka & Chittagong shall be standing against time waiting to be damaged by an earthquake of intensity VIII or IX in the area. In fact Dhaka city is being threatened by as many as 5 (five) and other major earthquakes of unknown return periods over next 500 (five hundred) years. Alarming indeed.

At present buildings in Dhaka city are being designed for an earthquake of intensity VII on the Modified Mecalli Intensity Scale which I categorically reject as this is an earthquake of moderate intensity where as intensity in Dhaka city during the Great Indian Earthquake of 1897 was VIII on the MMIS and my another fundamental question is what was the intensity in Dhaka city during Mega Earthquake in the year 1795? May be IX on the MMIS. As during this earthquake the entire landscape changed causing horizontal surface area to sink down with the formation of lakes ie haors and in other ares caused the horizontal  ground surface to rise up and down causing formation of Modhupur & Vaa-waal forest area i.e goars. Its return period is unknown.
Another fundamental striking technical point is that Dhaka was in the epicentral area during earthquakes of 1664,1828,1852,1864,1870 & 1885.

There is a very high probability that major earthquakes are striking Dhaka city at irregular intervals like Skoplje,Yugoslavia.On July 26,1963 the epicenter of the earthquake was only 10km from the city.The people of the city first felt vertical shocks and then the horizontal motion.
Skoplje experienced destructive earthquakes long ago in the years 518 and 1555, a gap of more than 1000 (one thousand) years and again in 1963,a gap of 408 years.

Another studies have revealed that Imperial Mogul Engineers & Architects were aware of the ways in which seismic forces cause a building to behave; taking this into account Mogul Imperial Constructions in the Northern India & Lahore,Pakistan and elsewhere have survived all the major earthquakes such as Taj Mahal built by His Imperial Majesty Emperor Shah Jahan.Kutub minar was destroyed but four minars at four corners of Taj Mahal survived as if guarding their imperial majesties with pomp with full military honor.
Not only that, the present day Atia Mosque located in the village Atia of Tangail,Bangladesh, following Mogul Engineering & Architecture built in the year 1406 have survived all the devastating earthquakes in the area including the Great Indian Earthquake, the Great Bengal Earthquake and Mega Earthquake in the year 1795.

So in view of the above circumstances a BUILDING TIME & PERFORMANCE NEED BASED SEISMIC ZONING MAP OF BANGLADESH will have more practical and realistic scientific and engineering value to save the country from catastrophic earthquake disaster(CED).
So at the moment we are having an inequation within an equation with respect to the seismic zoning map of Bangladesh currently in use which is rather misleading with respect to the seismic time frame for our region.

Therefore my propositions are now as follows based on the above line of reasoning & logic for  BUILDING TIME & PERFORMANCE NEED BASED SEISMIC ZONING MAP OF BANGLADESH for a period of next 500(five hundred) years and beyond that :

a) Considering seismic damage assessment over last 500 (five hundred) years
including major change in the landscape & formation of lakes with change in the
course of river flowing over land and also taking into account recent
Kashmir Earthquake & Sumatra Earthquake changing equilibrium conditions
within continental-continental convergence subduction interface and increase in
population & cost of land individual landowners and Builder/Developer may switch
over to construction of midrise & highrise residential & commercial buildings in
due course over the years in Dhaka,Narayanganj, Chittagong, Chittagong Hill
Tracts,Comilla,Sylhet,Mymensigh,Tangail,Bogra,Pabna,Rajshahi,Dinajpur &
Rangpur are to be brought under Zone-3 with earthquake intensity IX and
corresponding PGA value .55g

b) Rest of the towns & places excluding above places,cities & towns to be brought
under Zone -2 with probable earthquake intensity VIII and corresponding PGA  value
.30g

c) Zone-1 to be assigned with earthquake intensity of VII and corresponding PGA
value .15g

With regards and best wishes.

Engr.Sikandar Hayat Siddiqi
Project & Seismic Design Management Engineer /
Co-ordinator,Earthquake Anti-disaster Defence Management System Initiative (EADMSI) / Co-ordinator,Earthquake Monitoring & EADMSI Data Center
Dhaka - Bangladesh/Asia
Satellite Link International E-mail

---------------Original Message-------------

From : Prof Jamilur Reza Choudhury <vc[AT]bra...>
To     : Sikandar Siddiqi <sikandarsiddiqi[AT]yah...>,
Sent  : Sat, 22 Apr 2006 15:44:34 +0600
Subject : Seminar on Urban Earthquake Hazard at BRAC University on 24th April

"Prof. Jamilur Reza Choudhury" <vc[AT]bra...> wrote:
You are cordially invited to attend a seminar on "Urban Earthquake Hazard - Perceived Seismic Risk Preparedness in Bangladesh", jointly organized by American Institute of Bangladesh Studies, BRAC University and Bangladesh Earthquake Society on 24th April at 4 PM.
Speaker : Dr. Bimal Kanti Paul, Professor of Georgraphy, Kansas State University, USA
Venue : Room 104, BRAC University, 66 Mohakhali, Dhaka 1212

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